Conventional metal cutting technologies are well known in the art. For example, Oxy-Acetylene cutting technology has been used since the early 20th century wherein an oxygen and acetylene gas mixture is directed in a stream to burn through steel plate. Directed through torches at high pressure, the hot narrow gas stream actually combusts the material as iron burns easily at the high temperature used and the fuel gas supplied. This has been the traditional and fast way to cut iron and steel for over a hundred years. Oxy-Acetylene cutting technology can cut steel up to one foot thick into desired and specific shapes. Plasma cutting technology is a relatively new, circa 1970, cutting technology for cutting steel, mantels steel and aluminum where a stream of hot ionized gas is used to support an electric arc that burns and melts the material. This technology is up to ten times faster than an oxy-acetylene torch, however it is limited to metals under six inches in thickness and generally under two inches.
High Definition Plasma cutting technology is an improvement to plasma cutting technology with torches developed to cut sheet materials up to perhaps a half inch. This technology produces more accurate, narrow cuts in such thinner material. LASER cutting technology is a contemporary of plasma. In LASER cutting technology a highly focused laser beam is directed to the material and burns or melts the material. In some cases the laser may have gas assistance. LASER cutting technology has advantages over the other technologies as it requires much lower power, cuts with far greater precision, has a minimal cutting width and can cut a wide range of metallic and non-metallic materials including steel, aluminum, timber, plastic, etc. Water-Jet technology is another cutting technology developed in the 1970's, which uses abrasive compounds in a very narrow high speed water jet. Water-Jet technology is used principally on stone and ceramics but can also used for heat free cutting of thin metals.
The terms profile, path and contour are essentially equivalent terms for the collection of lines and arcs which make up the geometry of a part boundary. Usually paths are closed, whether internal or external. If they are unclosed internal paths, they are called ‘slits’. Unclosed external paths are problematic as it is not clear where the part exists until a path closes. Cutting of shapes is variously known as ‘profiling’ or ‘contouring’. Path is usually more specifically the contour followed by a cutting machine, where it is called a ‘tool path’ in the general NC parlance. A part consists of a single outside profile and perhaps multiple holes in the part which are described as internal profiles manufactured from a block or sheet of material referred to as a workpiece.
The term “edge start” refers to cutting that can start directly on the edge of a plate. In fact a pierce only serves to provide a hole which then allows edge cutting. This is distinct from cutting from the top, as in sawing. The idea of an edge start is to heat the edge to the required burning or melting temperature before moving into the material. This takes a delay at the edge. Some N.C. controls have this function available under standard coding but most require the machine to be instructed to stay over the edge for a specific time until the material is hot enough to cut. While edge starts are preferable, without continuous cutting, a pierce is generally needed for each part. An edge start can permit cutting of material thicknesses up to twice that possible if the material has to be pierced. The other advantage is that cutting can commence almost immediately by comparison with piercing as the whole edge of the material is able to be heated to ignition point at the same time. A corollary of this is that there is not explosion of molten material from the pierce hole and no overheating of the start area just to get through the material. In the art, an edge start is extremely advantageous but rarely used. In this invention, edge starts are automatically created for all parts in a nest.
The term kerf is representative of the radius of the hole created by a torch. This is typically half the width of a line cut with a round torch. Kerf is critical to cutting. Thus when cutting a shape, the torch center must be kept at least a ‘kerf’ distance from the shape profile so that the part cut is the right size. This offsetting of the desired shape to the center of the torch is known as ‘kerf compensation’ and is one of the more demanding fractions performed by an NC control. Also of note is that the thicker the material, the higher power that is required for cutting. As a result, the diameter of the cut increases and the larger the kerf becomes. Kerf can be very small on lasers and sheet metal, around 0.15 mm. With thick (say 2″ or 50 mm plate) it can be 4 mm for a total torch cut width of 8 mm.
In each of the foregoing cutting technologies, it is common practice to cut each part separately by creating a starting hole or “pierce” adjacent to the part and then proceeding to cut or separate the part from the surrounding material. However, there is significant cost associated with creating the pierce as it requires significant amounts of energy and time to cut through the material. Furthermore, the starting hole is extremely destructive and must be started a considerable distance from the part to avoid damaging the part both in the resultant shape of the part and the metallurgy of the heat affected area surrounding the pierce.
Generally in the art of cutting material, it is common that the cutting tool is optimized for cutting from an edge of material. Rarely is the cutting tool suitable for piercing material and often a separate process is used. Traditionally you have to pierce the material to create a hole for the edge cutting tool to work. To cut multiple parts, you have to create multiple pierces. Each pierce is time consuming, wasteful of material and damaging.
Hence, there is a need for a method and system that allows parts to be cut or separated from their surrounding material without the need of creating individual starting holes or pierces for each part.